An inverter is an electrical circuit that converts direct current (DC) to alternating current (AC). Inverters are used in a wide range of applications, from small switching power supplies in computers, to large electric utility applications that transport bulk power. In many applications, it is desirable for the inverter to boost a DC value and convert it into an AC waveform with high efficiency. In particular, it is desirable for maximum available power from a DC source to be delivered to a load with low harmonic distortion.
Due to their high efficiency and low power losses, multilevel inverters have been widely developed over the past few years. Multilevel inverters provide an AC waveform that exhibits multiple steps at several voltage levels. The closer the waveform comes to a perfect sine wave, the less likely it is that harmonics be present in the inverter's environment. Still, while multilevel inverter topologies are successful in reducing harmonics, they quickly become bulky and constricting when the number of voltage levels exceeds three, due to the large number of both active and passive components present in the circuit. In particular, several feedback sensors and pre-charged capacitors are typically used in these topologies, thereby increasing the risk of high voltage spikes during short circuit and faulty conditions. Also, since more DC supplies are used in multilevel inverters compared to conventional two-level inverters, bulky transformers and diode rectifiers are typically required, causing an increase in manufacturing costs. In addition, in order to allow the use of multilevel inverters in applications in which reliability, high security, and safety are required, topologies with isolated DC sources have been used where several isolated transformers and diode bridges are added to the DC side of the multilevel inverter. Industrial multilevel inverters may also be equipped with protection devices, such as voltage or current relays, to improve safety. However, with such solutions, implementation of complex voltage control strategies is often necessary, which proves costly and cumbersome.
Therefore, there is a need for an improved multilevel inverter.